I. Field of the Invention
This invention relates to an improved type of network communications adapter of the type used to provide high speed digital communications between a multiplicity of computing resources both co-located and geographically dispersed.
II. Discussion of the Prior Art
Prior art network communications adapters generally comprise one or more nodes where such node is the digital interface circuitry required to connect a computing resource, such as a computer a printer, or a mass storage device to the network. The computers may range from a super computer, such as the Cray II, a 64-bit main frame computer to any one of a variety of present-day 16-bit minicomputers. A single node may also accommodate a multiplicity of slower devices, e.g., 8-bit personal computers and terminals. The device/node interface is typically a high-speed parallel interface exemplified by the IBM block multiplexer channel type of input/output.
Within a local geographical area, the communication media preferably comprises one or more multi-drop coaxial serial data links or, alternatively, fiber-optic serial data links. This local connection will hereafter be referred to as the "trunk". A complete communication network may be comprised of a multiplicity of trunks which are linked together by commercial common-carrier communication services, e.g., telephone company T1-type trunk line. The network communication adapter functions to provide a virtual connection between a device coupled to the node and another device on another node to which the first device can present a request to communicate. The functions of a network communications adapter, well understood in the prior art, are as follows.
Data from the adapter's host is received, on demand, in a continuous or intermittent stream of data. This data stream is divided into a sequence of data blocks. To each block of data is added a message header identifying the source and the destination of the data block and following the data block is a message trailer providing error correction information. The data block with its associated header and trailer is called a message packet. By means of controlled contention with other network adapters, the transmitting adapter gains access to the trunk and link network resources required to transmit the message packet to the destination adapter. Message packets from a multiplicity of sources are sent in a time division multiplex manner over a single serial trunk or link network medium. Each network adapter screens all messages present on its trunk(s) and captures only those messages whose address matches the identification number of the adapter node. Each received packet is checked for correctness, the receipt thereof is acknowledged to the sender, the header and trailer are stripped off and the data formatted and presented to the receiving host computer or other digital device coupled to the receiving adapter.
Various techniques to assure data integrity even in the presence of noise and other perturbations on the network are well known in the prior art. In an ideal communication network, all devices would be able to communicate freely with any other devices in the network at their maximum data rate. In a real network, however, the data rate limitations of the trunk establish an upper limit on the number and rate of messages which can be accommodated. Any communication between devices through the network consumes a portion of this aggregate bandwidth regardless of the geographical distance spanned.
It is one object of this invention to provide a multi-node network adapter with a unique architecture which provides for very high data rate communication between the nodes of a given adapter without using the communication trunk, thereby conserving data bandwidth. With this invention, the aggregate data bandwidth of the network adapter can substantially exceed the aggregate bandwidth of the communication trunks employed.
In prior art communication systems, it is typically required that one of the host computers be designated as the network controller to manage or oversee message traffic across the entire network. The program which accomplishes this, the Network Executive, is generally run on a large main frame computer in a multi-tasking environment. For a large high performance network, the network executive can consume a significant fraction of the available computing capability of a relatively expensive main frame computer.
It is thus a further object of this invention to provide a novel communications adapter architecture in which a relatively inexpensive microprocessor can perform the network executive function.
It is a yet further object of this invention to provide a common, high-speed buffer memory which is shared by all of the node processors within a given network communications adapter.
A still further object of this invention is to provide a novel interrupt system which enables efficient coordination between the various node processors to facilitate the high speed flow of data messages.
Large telecommunication systems typically require a diverse range of communication interface hardware. One example might be a communications concentrator where a large number of slower speed devices are combined to appear as a single node on a communications trunk. In this case the channel bandwidth of the communications concentrator must be spread among a large number of interfaces. Another example is a "gateway adapter" which provides a communications bridge between two high-speed communication trunks. In this instance, all of the channel bandwidth is dedicated to a single communications path. In prior art systems, each type of communication device is typically a different product, each specialized to perform its particular function in the total system.
It is thus a yet further object of this invention to provide a network adapter which can be configured out of a common set of modular elements to perform a large number of different communications functions in that once configured, the aggregate channel bandwidth of the adapter can be selectively divided among various users to provide optimal throughput performance.